Apparatus and method for termination powered differential interface periphery

ABSTRACT

An apparatus and method for supplying power to the peripheral circuits of a transmitter circuit, especially an HDMI transmitter circuit, is disclosed. In an HDMI transmitter the termination resistors of the output driver are part of the receiver. DC power for the driver is supplied through these termination resistors. In prior art implementations of circuits this power, supplied by the receiver circuit, is wasted in the DC set-up circuit of the differential line driver. In various embodiments, this wasted power may be recovered from the remote termination to power selected peripheral circuits of the transmitter. The use of this wasted power may reduce the total system power consumption.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to the powering of peripheral devices through a remotely terminated differential driver load supply and more specifically to powering of peripheral circuits of an HDMI transmitter from the wasted power of the HDMI transmitter driver that is terminated at the receiver.

2. Prior Art

A typical high-definition multimedia interface (HDMI) transmission system 100 is shown in FIG. 1. The HDMI system has a source side driver 110 at the transmitter, with the drivers and the peripheral circuits, and a sink side termination 120 at the receiver. The twin differential drivers NL0 and NL1 of the source transmitter 115, driving the signal lines TXN and TXP respectively, are terminated through the termination resistors R0 and R1 connected to power supply at the receiver, or sink side termination 120. The termination is, for example, to the 3.3V nominal power supply per the HDMI specification. The transmitter drivers draw current from the receiver power supply through the termination resistors that enable the signal swing as per the HDMI specification. Since the drivers are differential they draw a constant DC current and consume power. Part of the power that is consumed is in the switching of the differential drivers and the rest is used for setting up the DC conditions of the drivers with a fixed voltage and/or current. This part of the power is typically wasted.

In the prior art the power supply to the peripheral circuits like pre-amplifier 111, PLL 112, serializer 113, and bias circuits 114, are from the power connection to the transmitter 110 from an external supply.

In the case of HDMI 1.2 standard, there are four transmission channels; each channel drawing 10.0 mA nominal current from the receiver's power supply. According to the HDMI specification the signal swing across the load termination is 0.4 to 0.6 V which leaves 2.7 V out of the typical 3.3V supply. This power is currently dissipated in setting up the DC conditions of the drivers and hence wasted. This power is available and can be tapped to power part of the peripheral circuits in the transmitter 110 as disclosed in this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the principles of the disclosed invention the following drawings are provided. It should be noted that driver termination power supply, typically being 3.3V, is designated in the drawings as VDD. Transmitter periphery power supply is designated Vdd in the drawings.

FIG. 1 is a block diagram of prior art HDMI driver with external power supply.

FIG. 2 is a block diagram showing an HDMI driver with power to peripherals supplied in accordance with the principles of the disclosed invention.

FIG. 3 is a schematic diagram showing the working principles of the disclosed invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An apparatus and method for supplying power to the peripheral circuits of a transmitter circuit, especially a high-definition multimedia interface (HDMI) transmitter circuit, is disclosed. In an HDMI transmitter, the termination resistors of the output driver are part of the receiver. DC power for the driver is supplied through these termination resistors. In prior art implementations, power supplied by the receiver circuit is wasted in setting the DC conditions of the differential line driver. It is suggested to use this wasted power from the remote termination to power selected peripheral circuits of the transmitter. The use of this wasted power of the line driver for powering the peripheral circuits reduces the total system power.

FIG. 2 is a non-limiting and exemplary HDMI video system 200 using the disclosed invention. The output drivers have sink side termination 120, including resistors R0 and R1, at the receiver, connected to the receiver's power supply. In a typical HDMI implementation, the output swing specification is 0.4 to 0.6V. For the typical differential driver pair, the specified current drive is fixed at 10 mA from the nominal value of the power supply, typically at 3.3V. There are four driver pairs in a typical HDMI transmitter, for example source side driver 110. Hence for a 0.6V swing specification, the current source of the driver has to dissipate 40 mA×(Vdd−0.6V). That means a minimum 1.8 Volt supply capable of driving close to 40 mA is available at the interconnected source of the differential driver transistors, NS0 and NS1. This available power can be used to power the peripheral circuits through a recovered and regulated power supply of the disclosure, with no impact on the total power drain of the sink receiver. This disclosure, by using the recovered power supplied through the termination, reduces the power dissipation of the transmitter and hence the total system. This supply voltage and current are regulated with circuitry 210, designed in accordance with the principles of the disclosed invention, to enable the utilization of this wasted power. The output of this circuit 210 is used to supply power to the standard peripheral circuits. In an embodiment of the current disclosure it is proposed to use this available power source of the HDMI transmitter driver, for peripheral circuits like pre-amps 111, the PLL 112, the serializer 113 and the individual bias circuits 114 of the HDMI transmitter which require, for example, a 1.2 V supply. The use of this disclosed method of recovering wasted power can reduce the power requirements of the transmitter and hence the total system power for a system comprising the transmitter and receiver.

In an exemplary and non-limiting case where the required supply is greater than 1.8V, it is still possible to use the wasted power with suitable voltage enhancing circuitry like a voltage booster 212. This is an optional element and can be eliminated when it is not required. The available current of this supply is the driver current and the available voltage is that at the interconnected source of the driver transistors, NS0 and NS1 of the differential drivers. It is hence necessary to use external circuitry 210 having the voltage regulator 213 to regulate the voltage and bias control circuit 211 to sink the required total 40 mA required by the differential drivers, through the ground terminals of the peripheral devices powered by this supply.

Reference is now made to FIG. 3 that shows the principle of operation of the current invention. It is necessary for the driver current of the differential driver transistor pair comprising NS1 and NS2 to be at a pre-defined value, for example the value of 10 mA/pair, to adhere with the requirements of the HDMI specification. In order to achieve this, a bias control circuit 211 with current sensing elements and current control is used. This circuit functions as follows. Current sensing elements G1 310 and G2 320 are voltage controlled current sources with a gm proportional to 1 and N−1 providing a gm ratio of 1:N−1. Examples of G1 and G2 are MOSFET or BJT devices. It is possible to use more than two voltage controlled current sources, but at least two are necessary. The startup circuit 240 is necessary to enable the circuit to start operating when the output is connected and the termination is enabled. This start circuit 240 taps or bleeds a small amount of power from the termination circuitry as soon as connection is made to the remote termination, to generate a Vbias voltage for G1 310 and initiate the operation of the bias control circuit 211. The voltage controlled current source G1 310 acts as a reference current sensor and control, with a fixed current source 330 of Idrv/N coupled to it. The voltage developed across the current source 330 is fed to the control pin, CTL of the shunt regulator 340. The shunt regulator 340 forces the voltage at its input pin, IN, to equal to that at its CTL pin by shunting the current through it. In doing so, the current passing through the shunt voltage controlled current source G2 320, will be equal to N−1 times the reference current in G1 310, which will be (N−1)*Idrv/N. Once the bias is operational, the startup circuit 240 is removed from the operation making the total current passing through the driver to be fixed at Idrv, from both the voltage controlled current sources together, enabling the full driver current. The current through G2 320, with the voltage at the source of the device G2 320, is then available as output of the bias control circuit 211, for use as supply voltage. After regulation by the voltage regulator 213 this recovered power, voltage and current, can be used to power the peripheral circuitry.

This voltage can also be boosted, if necessary, by the voltage booster 212, prior to regulation in the voltage regulator 213. This recovered and regulated supply voltage can then be used by any peripheral circuitry that requires higher than the voltage available at the source of the shunt voltage controlled current source G2 320.

A person skilled-in-the-art would readily appreciate that the invention disclosed herein is described with respect to specific embodiments. However, this should not be considered a limitation on the scope of the invention. Specifically, other implementations of the disclosed invention are envisioned and hence the invention should not be considered to be limited, for example, to HDMI compatible termination devices. Rather, the scope of the disclosed invention is as broad as its claims and the powered termination suggested herein may be used in other applications and configurations. 

1. A power recovery circuit of a transmitter for recovering power from the terminating resistors of a termination power supply comprising: a bias control circuit having at least a pair of current sensing and control elements coupled to connected sources of a differential driver pair to provide a predetermined bias to the connected sources, the differential driver pair being coupled to the terminating resistors; a startup circuit coupled to the terminating resistors, the startup circuit enabled to provide an initial starting bias voltage and current to the bias control circuit when the termination power supply is enabled; and a voltage regulator having an input coupled to an output of the bias control circuit to regulate an output voltage of the power recovery circuit; the power recovery circuit using current supplied to the differential driver pair from the termination power supply and the voltage at the connected sources of the differential driver pair to provide regulated power from the voltage regulator to at least a portion of the peripheral circuits of the transmitter.
 2. The power recovery circuit of claim 1 wherein the bias control circuit provides a predetermined bias to the connected sources by controlling power not used by the voltage regulator to supply power to the peripheral circuits.
 3. The power recovery circuit of claim 1, further comprising: a voltage booster coupled between the bias control circuit and the voltage regulator to step up the voltage to the voltage regulator.
 4. The power recovery circuit of claim 1, wherein the terminating resistors are terminated in a remote receiver power supply.
 5. The power recovery circuit of claim 4, wherein the receiver is an HDMI receiver.
 6. The power recovery circuit of claim 1, wherein the transmitter is an HDMI transmitter.
 7. The power recovery circuit of claim 1, wherein the current sensing and control elements comprise voltage controlled current sources.
 8. The power recovery circuit of claim 7, wherein the voltage controlled current sources are selected from a group of elements comprising: MOSFET devices and BJT devices.
 9. The power recovery circuit of claim 1, wherein the startup circuit bleeds a small amount of power from the termination power supply to start the bias control circuit.
 10. The power recovery circuit of claim 1, wherein the startup circuit is configured to be disabled from the bias control circuit once the bias conditions have been established. 